A whistle tone is the highest register of the human voice, lying above the modal register and falsetto register. It is created by using only the back of the vocal folds, and the lower part of the whistle register may overlap the upper parts of the modal and falsetto registers, making it possible for singers to phonate these notes in different ways. The whistle register is the highest phonational register, that in most singers begins above the soprano "high D" (D6 or 1174.6 Hz) and extends to about an octave above (D7 or 2349.3 Hz). The physiology of the whistle register is the least understood of the vocal registers, and it is difficult to film the vocal cords while they are operating in this manner as the epiglottis closes down over the larynx, and the resonating chamber assumes its smallest dimensions.

Whistle tones are often confused with what’s called the Super Head Voice. Singers can achieve very high notes with the Super Head Voice by singing in their normal falsetto range and then forcing more air through the vocal cords to increase the range of the notes. Whistle Tone is slightly different in the sense that it is a different technique, only using a very small part of the vocal cords to hit that whistling tone. The Mariah Carey whistle tone is the arguably the standard bearer for Whistle Tones in modern music.

Whistle tones are not easy to produce, and it can put some strain on your voice, so it is important to take your time and practice gradually. There are several exercises that can help singers develop their whistle tones, such as the Yawny-Whistle technique, which involves taking a low breath from the diaphragm and pretending to yawn to relax the throat and jaw.